Tau Reconstruction Overview in Particle Physics Research

1. Offline tau reconstruction overview M. Pilar Casado (IFAE & UAB) • Introduction • tauRec • tau1P3P • AOD and ESD • Conclusion

2. tDecays ~35%, but they belong to another story • t decay modes • Leptonic decay modes • t nt + ne + e (17.4%) • t nt + nm + m (17.8%) • Hadronic decay modes • 1 prong • t  nt + p± (11.0%) • t  nt + p± + p0 (25.4%) • t  nt + p± + p0 + p0 (10.8%) • t  nt + p± + p0 + p0 + p0 (1.4%) • t  nt + K± + np0 (1.6%) • 3 prong • t nt + 3 p± + np0 (15.2%) How to identify them? 77% 23%

3. Introduction

4. Practical info • tauRec: • Authors: D. Cavalli, S. Resconi, F. Paige, S. Rajagopalan, M. Heldmann. • Documentation: • Code: http://atlassw1.phy.bnl.gov/lxr/source/atlas/ Reconstruction/tauRec/ • Wiki page: https://uimon.cern.ch/twiki/bin/view/Atlas/ TopologicalClustering?topic=TauRec • Status in the offline releases: Part of the offline reconstruction. • tau1P3P: • Authors: E. Richter-Was, T. Szymocha, L. Janyst. • Documentation: • Code: http://atlas-sw.cern.ch/cgi-bin/viewcvs-atlas.cgi/users/erichter/ • Web page: http://project-tau1p3p.web.cern.ch/project-tau1p3p/ESDtau1P3P/index.html • Status in the offline releases: Still not included.

5. tauRec • Reconstruct t-candidate: • Start from different objects: CaloClusters (default), Isolated tracks, … • Associate tracks from the TrackParticle container to the candidate • Build the set of variables for t-identification, and then calculates Likelihood(s) • Calibrate candidates • Apply set of the basic cuts for t-identification

6. Some tau variables • Some variables calculated in offline (and in the trigger!):

7. From M.Heldmann Variables used in tauRec • Builds set of variables for t-identification – they are pT dependant • Calculate Likelihood from: REM, FISO, Ntrack, Strip Width, Nstrip, Charge, Impact parameter, ET/pT(1sttrack) REM FISO Charge Ntrack Nstrip Impact parameter Strip Width ET/pT(1sttrack) SignalA→ttbackground QCD, 0<pT<44 full line and 134<pT< 334 dashed line

8. From E. Richter-Was et al. Tau1P3P (I) • Motivation: • Tau1P3P dedicated to the tau identification in searches for the light Higgs or soft SUSY: t's with ETvis = 20-70 GeV. • Explores exclusive features of the t lepton: • hadronic t IS NOT a jet but 1 track + 0 or 3 tracks + 0 • Decay products well collimated in space, track direction can provide precise estimate for direction, if track sufficiently dominant. • energy scale defined from energy-flow and not calorimetric. • Publications: • 1. E. Richter-Was, H. Przysiezniak and F. Tarrade, ATL-PHYS-2004-030; • 2. E. Richter-Was, T Szymocha, ATL-PHYS-PUB-2005-005. • 3. D. Froidevaux et al., ATL-COM-PHYS-2005-024 • 4. E. Richter-Was, L. Janyst ATL-COM-PHYS-2005-008

9. tau1P3P (II) in “real life” we will probably start from regions indicated by calorimetric clusters above ETcut identify “good quality” hadronic track, pT > 9 GeV, find nearby “good quality” tracks with pT > 2 GeV in DR < 0.2 t3P t1P 2 nearby tracks (h,f) from bary centre of tracks S charge = +-1 no nearby-track (h,f) from track at vertex build ETeflow, use DR < 0.2 build ETeflow, use DR < 0.2 build discrimination variables use DR < 0.2 as a “core”, 0.2 < DR < 0.4 for isolation only build discrimination variables use DR < 0.2 as a “core”, 0.2 < DR < 0.4 for isolation only • t1P - single-prong candidates • t3P - three-prong candidates

10. tau1P3P (III) with D. Froidevaux, for more details see talk at Nov. 2004 Physics Week ETeflow= ETemcl +ETneuEM + S pTtrack + ... used only EM cells within DR < 0.2 around tau1P direction ETeflow/ETtruth ETeflow/ETtruth 1 prong 3 prong good resolution: ETeflow/ETtruth t1P: 65.2% in 0.9-1.1 88.3% in 0.8-1.2 t3P: 73.4% in 0.9-1.1 93.8% in 0.8-1.2 good stability for ETtruth = 20 – 70 GeV <>=1.011 s = 0.0303 <>=1.014 s =0.0663 ETeflow/ETtruth ETeflow/ETtruth 1.2 1.2 0.8 0.8

11. Comparison of performance

12. Present AOD class for tau’s:TauJet.h • inherits from P4EEtaPhiM class, • access to asociated tracks, • access to associated CaloCluster, • access to associated Vertex • numTracks (use also for tau1p, tau3P) • pEM 4-momenta of EM component • other attributes set by the ”author” author=tau1P3P already implemented

13. Present ESD class for tau’s:TauObject.h • trying to integrate different basic principles of both algorithms • access to associated cluster, tracks, vertex can be easily made common • several variables are very specific for tauRec, and other for tau1P3P possible approaches:  create “author” like for AOD ?  inherit from a basic class, different concrete classes ?  add more variables/methods ? Details being discussed at the moment in the Tau group.

14. Conclusion • There are two algorithms for tau reconstruction in the offline: tauRec (cluster and track seeded algorithm) and tau1P3P (track seeded algorithm). • There are many common variables: EM radius, Strip width and fracETR12. • Key differences: • H1 calibration vs energy flow. • Likelihood vs PDE-RS. • Energy resolution is similar for both packages. Efficiency is better for tau1P3P for ET < 25 GeV. • Whilst AOD is quite defined in the offline tau reconstruction, the ESD class is under discussion.